The influence of iron content on the promotion of the zircon structure and the optical properties of pink coral pigments

A sol–gel reaction starting from Si and Zr alkoxides, in water-ethanol mixtures, was employed to obtain iron doped zirconium silicate powders (zircon). The starting amount of the ferric salt in the sol–gel reacting mixture was varied in order to obtain Fe2O3/Zr molar ratios in the range 0.7–10%. The products of the sol–gel reaction were calcined in the range 800–1300 °C. X-ray diffractograms, EDX analyses and diffuse reflectance spectra were obtained and analysed for all the calcined powders; the colour of the pigments was characterised on the grounds of the CIE (Commission Internationale de l’Eclairage) standard procedure (CIE L∗a∗b∗ measurements). Results from the structural and spectral characterisations are examined and cross-compared to produce a consistent picture of the role played by iron on the promotion of the zircon lattice and on the optical properties of the reaction products.